Die and punch sets

ABSTRACT

In a method of extruding a metal billet, the billet is positioned in a hollow die and a punch is caused to enter the die to extrude metal from the billet. One of the extrusion tools defined by the punch and the hollow die is formed with an operative surface of hot pressed silicon nitride and the extrusion operation is performed without effecting a prior lubrication treatment to the metal billet.

United States Patent Lawson Aug. 26, 1975 0112 AND PUNCH SETS 2,882,759 4 1959 Altwicker 76/107 A 4 3,443,41 l 5/!969 Anthony v v t 72/267 [751 F' Lawson 3,561,242 2/i97l Biginclli .1 72/267 Blrmmghami Engldnd 3.752218 8/l973 Gamble etal. .1 l64/l38 {73] Assigne Joseph Lucas (Industries) Limited,

Birmingham England FOREIGN PATENTS OR APPLICATIONS 970,639 9/1964 United Kingdom 1. 423/344 [22] 1974 1,092.637 ll/l967 United Kingdom 423/344 [21] Appl. No: 435,471

Related Application Dam Primary Examiner-Richard J. Herbst [62] Division of Ser. No. 246548 April 24, 1972, Pat. Attorney, Agent. or FirmHolman & Stern (30] Foreign Appllcatlon Pr|0r|ty Data ABSTRACT Apr, 27, I971 United Kingdom ll509/7l In a method of extruding a metal billet. the billet is po I52] 72/253 sitioned in a hollow die and a punch is caused to enter I5 1] 'f B21C 23/00 the die to extrude metal from the billet. One of the ex- [58] F'eld of Search 72/253- trusion tools defined by the punch and the hollow die 72/267 354 359, 467, 476, 479; 76/l07 R; is formed with an operative surface of hot pressed sili- 423/344; 425/88 con nitride and the extrusion operation is performed without effecting a prior lubrication treatment to the [56] References Cited metal m UNITED STATES PATENTS 2 6l8 565 [H1952 Nicholson 423/344 8 Claims, 3 Drawing Figures PATENTEU K115251975 1 1801061 FKil.

DIE AND PUNCH SETS This invention relates to a method of extruding a metal billet and is a Divisional Application from my copending application Ser. No. 246,548 filed Apr. 24, 1972, now US. Pat. No. 3,807,212.

In known techniques for extruding metal billets, the extrusion is effected by means of a die set having a punch and a hollow die each formed of steel or tungsten carbide. However, a disadvantage exists with the known die sets in that before a metal billet can successfully be extruded the billet must undergo an involved, and therefore lengthy lubrication treatment. The conventional lubrication treatment in the case of a steel billet includes removal of grease from the billet followed by an acid pickling process, which prepares the billet for a subsequent phosphating and soaping treatment. In particular, the phosphating treatment is required so that a parting layer is produced between the billet and the components of the die set since without phosphating, localised welding between the billet and the components of the die set can result. The soaping treatment lowers the friction between the billet and the components of the die during relative movement between the punch and the die, whereby the punch load required to efi'ect the extrusion, and hence the stresses within the die set, are reduced. It has now been found that if the die and/or the punch are formed of hot pressed silicon nitride, then the use of the lubrication treatment described above, prior to extrusion, can be avoided.

Accordingly, the invention resides in a method of extruding a metal billet comprising the step of positioning the billet in a hollow die and causing a punch to enter the die to extrude metal from the billet, the improvement comprising:

Producing at least one of the extrusion tools defined by the punch and the hollow die with an operative surface formed from hot pressed silicon nitride and performing the extrusion operation without effecting a prior lubrication treatment to the metal billet.

[N THE ACCOMPANYING DRAWINGS FIG. 1 is a sectional view illustrating an extrusion process using a die and punch set according to a first example of the invention.

FIG. 2 is a sectional view illustrating an extrusion process using a die and punch set according to a second example of the invention, and

FIG. 3 is an exploded part sectional view of a punch assembly incorporating the punch shown in FIG. 2.

Referring to FIG. 1, in a first example of the invention a steel component 11 is produced by performing an impact extrusion operation on a bright drawn steel billet (not shown) using a first die and punch set 12. The die and punch set 12 includes a hollow die 13 formed of hot-pressed silicon nitride and a punch 14 formed of tungsten carbide. The hot-pressed silicon nitride die 13 is formed by heating silicon powder to a temperature not exceeding 1,300C in a non-oxidising atmosphere containing nitrogen, whereby the silicon powder is converted into silicon nitride which is substantially entirely into the aphase. The silicon nitride powder is next intimately mixed with not more than 1 percent by weight of magnesium oxide by wet ball milling in butanol for a period of 72 hours. The mixed powder is then formed into the hollow die 13 by pressing the powder between graphite dies at a temperature not exceeding 1650C and at a pressure of 4000 lbs per square inch. In use, a conventional metal shrink ring is fitted around the die 13 so as to ensure that the silicon nitride of the die is under compression.

The arrangement of the die and punch set 12 is such that when the billet is inserted into the die 13 and the punch 14 is moved into the die to effect the impact extrusion process, metal from the billet flows in the direction of movement of the punch 14 to produce the component 11. Using the die and punch set 12 it is found that the extrusion of metal from the billet can be successfully effected without the initial lubrication of the billet by conventional phosphating and soaping treatments. Further, as shown in the drawing, the die and punch set 12 includes an ejector punch 15 by means of which the extruded component 11 can be removed from the die.

As shown in FIG. 1, the bore in the silicon nitride die 13 used in the above example is stepped to define a wide portion and narrow portion, metal flowing into the narrow portion of the bore during the extrusion process to produce the component 11. In a modification of the above example, however, the die 13 is defined by an outer sleeve formed of tool steel, such as is used in conventional extrusion dies, and an annular insert formed of hot pressed silicon nitride which is positioned in the bore in the outer sleeve so that the bore in the assembled die 13 is stepped as shown in FIG. 1.

Referring now to FIGS. 2 and 3, in a second example of the invention a second die and punch set 16 is used to effect a further impact extrusion process on the component 11, after the initial extrusion by the die and punch set 12. The die and punch set 16 includes a hot pressed silicon nitride punch 17, formed in a similar manner to that described for the die 13, and a die 18 formed of high speed steel type B.S.S. M2, the set 16 being arranged so that when the punch 17 is moved into the die 18 metal from the component 11 flows in the opposite direction to the direction of movement of the punch 17. This type of extrusion process is known as a backward extrusion, as distinct from a forward extrusion where, as in the first example, metal is caused to flow in the direction of movement of the punch effecting the extrusion. Thus, to produce the required metal flow, the end 19 of the punch 17 which enters the die 18 to effect the backward extrusion is of conical form with an angle of being defined at the apex of the cone. Since the punch 17 is formed of hot-pressed silicon nitride, it is necessary to ensure, if the punch is to have a long working life, that the only forces acting on the punch in use are compressive forces rather than tensile forces. Thus, the body of the punch 17 adjacent the end 19 is tapered with a very fine surface finish, that is in the region of between 2 and 5 micro inch for the average height of peaks on the surface, and without any additional shaping which is often incorporated in a backward extrusion punch to enhance metal flow. It will be appreciated that the body of the punch 17 is tapered in order to facilitate removal of the component from the punch after the operation without imposing on the punch tensile stresses in excess of that which the punch can accommodate In this particular example the body taper is in the order of a 7 included angle. The silicon nitride punch 17 is supported by a steel, punch carrier member 21 and defines with the carrier member 21 and a steel backing member 22 a punch assembly 23. The punch 17 is removable from the punch assembly 23 so that ready replacement of the punch 17 is possible. As in the previous example, when the die and punch set 16 is required to effect impact extrusion of the component 1 1, it is found that the extrusion process can be successfully effected without initial lubrication of the component by the standard phosphating and soaping treatments. Further, as in the example de scribed above, in order to facilitate removal of the component after the extrusion process, the die and punch set 16 includes an ejector punch 24.

It is to be appreciated that in the first example the punch 14, as well as the die 13, could be formed of hotpressed silicon nitride, and also that in the second example, the die 18, as well as the punch 17, could be formed of hot-pressed silicon nitride.

l claim:

1. A method of extruding a metal billet comprising the steps of producing at least one of the extrusion tools defined by a punch and a hollow die with an operative surface formed from hot pressed silicon nitride and, without effecting a prior lubrication treatment to the metal billet. positioning the billet in the hollow die and causing the punch to enter the die to extrude metal from the billet.

2. A method as claimed in claim 1 comprising the step of forming the hollow die bore of hot pressed silicon nitride with a wide portion communicating with a cross-section substantially complementary to the wide portion and extruding the metal billet so that metal of the billet flows in the same direction as the direction of movement of the punch during extrusion.

3. A method as claimed in claim 2 comprising the step of forming both the die and the punch with operative hot pressed silicon nitride surfaces.

4. A method as claimed in claim 1 comprising the step of forming the terminal end of the punch of hot pressed silicon nitride with a conical tip and an angular relief immediately therebehind, and extruding the metal billet so that the extruded metal of the billet reverse-flows in relation to the punch as it is being extruded.

5. The method as claimed in claim 4 including the step of forming the conical tip of the punch at an angle of 6. The method as claimed in claim 4 comprising forming the angular relief in the order of a 7 included angle with respect to the outer surface of the punch.

7. The method as claimed in claim 1 comprising forming the hollow die with a hot pressed silicon niitride insert forming the one silicon nitride surface.

8. The method as claimed in claim 4 including the step of finishing the conical terminal surface and the relief therebehind to an extremely fine degree and substantially to from 2 to 5 micro inches for the average height of peaks on the surface whereby metal flow is enhanced during impact-extrusion. =1 3 

1. A method of extruding a metal billet comprising the steps of producing at least one of the extrusion tools defined by a punch and a hollow die with an operative surface formed from hot pressed silicon nitride and, without effecting a prior lubrication treatment to the metal billet, positioning the billet in the hollow die and causing the punch to enter the die to extrude metal from the billet.
 2. A method as claimed in claim 1 comprising the step of forming the hollow die bore of hot pressed silicon nitride with a wide portion communicating with a cross-section substantially complementary to the wide portion and extruding the metal billet so that metal of the billet flows in the same direction as the direction of movement of the punch during extrusion.
 3. A method as claimed in claim 2 comprising the step of forming both the die and the punch with operative hot pressed silicon nitride surfaces.
 4. A method as claimed in claim 1 comprising the step of forming the terminal end of the punch of hot pressed silicon nitride with a conical tip and an angular relief immediately therebehind, and extruding the metal billet so that the extruded metal of the billet reverse-flows in relation to the punch as it is being extruded.
 5. The method as claimed in claim 4 including the step of forming the conical tip of the punch at an angle of 170*.
 6. The method as claimed in claim 4 comprising forming the angular relief in the order of a 7* included angle with respect to the outer surface of the punch.
 7. The method as claimed in claim 1 comprising forming the hollow die with a hot pressed silicon niitride insert forming the one silicon nitride surface.
 8. The method as claimed in claim 4 including the step of finishing the conical terminal surface and the relief therebehind to an extremely fine degree and substantially to from 2 to 5 micro inches for the average height of peaks on the surface whereby metal flow is enhanced during impact-extrusion. 